An integral part of an aircraft fuselage is the door assembly through which passengers and crew enter and exit the aircraft. One type of aircraft door that has become increasingly popular for use with commercial aircraft is the translating motion door. A translating motion door, when opened, first moves upwards and slightly away from the opening in which it was seated. The door is then moved outwards, away from the opening so as to allow passage through the opening.
Translating motion doors have taken the place of aircraft cocking doors. A cocking door is rotated inwards and then moves diagonally outwards of the fuselage opening with which it is associated. A translating door does not swing into the space adjacent the egress way inside the aircraft to the same extent that a comparable cocking door swings into this space when it is opened. When a cocking door is installed on an aircraft, this space must be kept clear to insure that the door can freely open. In comparison, when a translating door is installed there is no need to keep this space clear; interior units such as galleys, lavatories and even seats can be placed in the aircraft much closer to the egress way. Thus, the installation of a translating door onto an aircraft makes it possible to enhance the utilization of the space inside the aircraft. A translating door is also smaller in size and lighter in weight than a cocking door used to seal the same sized opening. Moreover, a translating motion door is typically assembled out of fewer components that are less expensive to manufacture than that of a comparable cocking door. Another advantage of a translating door is that it moves along a relatively horizontal path when opened. In comparison to the upwards movement of a cocking door, this feature makes the translating door much easier to open. This feature is important because cabin attendants, who are often small in stature, sometimes find it physically strenuous to open a cocking door.
Aircraft doors, including translating doors, are held in place by stop pins which extend outwards from the door that abut complementary stop pads extending from the fuselage in the door opening. When an aircraft is in pressurized flight, the interior fuselage pressure serves to urge the door outwards; the stop pins are held in place against the stop pads so as to hold the door in place. The opening and closing of a translating motion aircraft door is controlled by a latch lock mechanism. The latch lock mechanism opens the door by initially raising the door so that stops on the door clear complementary stops that extend into the fuselage opening. Once the stops are cleared, the latch lock mechanism moves the door away from the fuselage so that it can be moved free of the opening. The movement of the door away from the opening clears the opening so as to allow persons to enter and exit the aircraft. The latch lock mechanism is used to close the door by reversing the motion used to open the door. The latch lock mechanism also prevents the door from opening once it is closed. In order to be suitable for use in a commercial aircraft, a latch lock mechanism must be configured so that a cabin attendant with relatively low body strength can actuate the mechanism so as to lift open a door that may weigh 350 pounds or more.
A disadvantage of many aircraft door latch lock mechanisms for translating motion doors is that the movement of the mechanism is controlled by a handle that pivots about an axis that extends laterally across the aircraft. The difficulty with these mechanisms is that at some point during the opening of the door it is necessary to move the handle downwards, while the latch mechanism is working to move the door upwards. In other words, the person who is trying to open the door by moving it upwards finds it necessary to exert a downwards force on the door. This mechanical inconsistency increases the overall physical strength required to open the door.